Making a Customized 3D Printable Foot Model (.stl)

Introduction:

If your are a maker, and trying to make customized things to fit your feet, this tutorial will help you make a 3D printable, 1:1 sized, foot model.

3D printers are famous for their abilities to create customized models and rapid prototyping. Having a digital model of your feet will kick-start your custom fit projects or applications. For example, you can make slippers, in-soles, and high heels which only fit in "your size".

The whole process of creating this model can be finished in 1 to 2 hours depending on your computer's performance and Internet speed. (I spend about 1.5 hours.)

Pre-request:

Download “123D” app on your smart phone, and download “Meshmixer” on your computer as well.

You can download the applications here:

123D: http://www.123dapp.com/catch
Meshmixer: http://www.meshmixer.com/

Tools & Materials:

A smart phone (ios, Android, or Windows)
A computer (laptop is okay)
A friend (or a stranger who is willing to spend 5 minutes taking pictures of your feet)
A Cardboard box (You need something to secure your feet)

Step 1: Prepare to Use 123D

All you need to know about 123D for now:

The “123D” app allows you to take photos (usually about 28 to 70 photos) around objects (your feet). Then, it will send these photos to an Autodesk cloud server and return a 3D mesh object (file) as a result.

Preparation:

Find a partner. (You will need a teammate to take photos of your feet.)
Download “123D” app from app store: (http://www.123dapp.com/catch)
- Open the app and Login.
  - This app requires an Autodesk account, please register if you haven’t got one.
Find a location for photo shooting.
- Location should have good lighting conditions (prefer natural lights).
- NO transparent or reflective objects in the photos (cover them with a blanket).
- Fewer objects in the background will get a better result.
Find a good position to “show off” your feet
- Your feet should NOT be moving or shacking during the picture taking process.
- "A good position" example:
  - Lie down on your belly and curl your knees to 90 degrees.
  - Use a cardboard to secure your feet in a fixed position if necessary.
  - (Forgive me for not showing a picture of my posture. Trust me you don't want to see it.)
Place an reference object.
- A ruler is a good reference object (or anything with known dimensions) as shown in the picture above.

Caution: Reference Object is important for later operations in Meshmixer.

Step 2: Start Capture Your Feet

Open “123D”
“start a new capture” (press the “+” on the top right)
You should be taking about 34 to 50 photos.
- Caution: Keep your shadows away from the photos.
When done, review each photo.
- Make sure the feet are in the center of each photo.
- Make sure there are NO blurring photos.
Submit
- Caution: It may take more than 20 minutes to have a result, so be patient.
When a result is posted in your Autodesk account
- Move on to step 3!

Step 3: Using “Meshmixer” to Adjust the Mesh Object (your Feet)

All you need to know about Meshmixer for now:

We will use Meshmixer to create a 1:1 ratio mesh object. Then the object can be exported as a “.stl” type file. This STL file can be used to print 3D objects on almost any 3D printer.

Helpful Link:
If you really want to learn Meshmixer, you can find official tutorials here: https://www.youtube.com/user/meshmixer/videos

Otherwise, follow this tutorial, and you will be fine.

Preparation:

1. Open “Meshmixer” and import the file

Click on the “123D cloud” button
A window should pop up and ask you to sign in if you haven’t.

2. Click on “My projects” >> Select the file you want to import >> Click “Import”

Caution: This may take some time.

Step 4: Crop the Mesh Object:

Toolbar is on the left side.
- Tip: Use scroll wheel to zoom in and out. Use right click and drag to adjust view.
Click “Edit” >> “Transform” (press T for shortcut)
- To move and rotate the object around, click and drag the “arrows” and “arcs” to adjust.
- You may not recognize your feet in this picture, because lots of background objects have been captured.
To cut out the background materials, click "Select" (“S” for shortcut) and click on four points in space (as shown in the 2nd screenshot above).
Meshmixer will highlight your selection (as shown in the 3rd screenshot above).
Hit “delete” on your keyboard.
Repeat step 3 to 5 until you have a clean mesh object of your feet and the reference tool (as shown in the last screenshot above).
Save the file

Click “File” on top left corner >> Click “Save” >> Name it “both_feet.mix”

Caution: Make a copy of this file in case you mess up.

Step 5: Find the Scale Factor:

In order to find the scale factor we need a reference object. Because the feet object I imported into Meshmixer is NOT 1:1 ratio comparing to my real feet, and also because I cannot get an accurate measurement of my feet due to their dynamic and complex shape, I have to place a reference object (ruler) in the photos.

Open the file we just saved, “both_feet.mix”.
Crop the object and leave only the ruler.
Use “Transform” again to rotate the ruler, so that its “adjacent edge” is parallel to the x-axis as shown above.
Use “Transform” to scale the ruler:
- We know the "adjacent edge" of this ruler is 154.5mm.
- Click on the number and change it to "154.5".
- Hit "Enter"
Record the scale factor:
- The value of the scale factor is shown by the value of "Scale X".
- In this case, it is "19.637".
Save the file:
- Click “File” on top left corner >> Click “Save as” >> Name it “reference.mix”

Tip: Remember your scale factor! Take a screenshot if needed.

Step 6: Scale and Create a Printable Model of My Left Foot:

Open the file, “both_feet.mix”.
Crop the object and leave only the left foot.
Uniform the color of my left foot model:
- Click "Shaders"
- Drag and drop the "grey" color onto the model.
Perform a plane cut so that the model has a flat base:
- Click "Edit" >> "Plane Cut"
- Hold on click and drag the dark blue arrow to adjust height.
- Hit "Accept".
Transform the model to its original size:
- Use "Transform"
- Under "Scale X", enter the scale factor "19.637".
Reduce the resolution of the model:
- Click "Select" >> "Select All" (hit ctrl A)
- Go to "Edit" >> Click "Reduce"
- From "Reduce Target" select "triangle budget" & keep "shape preserving"
- Under "Tri Count" enter the number of triangles you want, and hit "Enter"
  - Usually the number is between 5,000 to 10,000.
  - In this case, the number of triangles is "6500".
Export the model as a STL file:
- Click "Export" and Save it as "STL Binary Format".
Repeat the steps 1 through 7 for the right foot to create a right foot model.